Pump assemblies to be mounted on a container containing a foamable liquid, which upon actuation provide a foam are well known in the art. For instance, U.S. Pat. No. 5,443,569 discloses such dispensing assembly, the contents of which are herein incorporated in its entirety by reference.
This known dispensing assembly comprises a liquid piston pump and an air piston pump concentrically arranged with respect to each other. The cylinders of the liquid and air pump are formed by the inner cylinder and outer cylinder of a double cylinder, respectively. The dispensing assembly further comprises a common actuation button for simultaneous actuation of the liquid pump and the air pump by manual depression of the actuation button. A liquid piston and an air piston are reciprocally movable arranged in the liquid and air cylinder and are operatively connected to the actuation button so that upon actuation of the actuation button the liquid piston and the air piston may reciprocally be moved in the liquid and air cylinder, respectively.
When the above dispensing assembly is mounted on a container containing a foamable liquid, this liquid may be drawn out of the container by actuation of the actuation button. At the same time air will be pumped by the air pump. The pump outlets of the liquid and air pump are connected to a mixing chamber where the liquid and air is mixed to a (pre)foam. The mixture of liquid and air is consequently pumped through a dispensing channel and passes one or more porous elements, for instance sieves, to form a homogeneous foam which is dispensed at a dispensing opening at the end of the dispensing channel.
Although the above pump has been shown to be very successful in the market for a variety of foamable liquids, such as soap, shampoo, dishwashing detergent and sun cream, there may still be some further improvements possible. Furthermore, since the dispensing assembly of the above type is more and more applied as a mass product there is a continuos strive for simplification, while maintaining a good foam quality.
Generally, it is desirable to dispense a desired quantity of foam per stroke of the actuation button. Further, the length of a stroke is limited for handheld foam dispensers since the actuation button is depressed by a finger while the dispensing device is held by the same hand. Due to the required diameter of the double cylinder to dispense a certain quantity of foam and the limited stroke, the neck opening of the container has to be of a certain minimum diameter to receive the double cylinder of appropriate size. In some applications it is desirable to use containers having a neck opening with a smaller diameter, while maintaining the same stroke length and the same quantity of foam dispensed per stroke. The known dispensing assembly design until now cannot fulfill these requirements on dispensing quantity and dimensions.